Manufacture of cellulose from ligno-cellulosic products



Patented Feb. 16, 1937 UNITED STATES MANUFACTURE OF CELLULOSE FROM LIGNO-CELLULOSIC PRODUCTS Henry Dreyfus, London, England No Drawing. Application February 28, 1934, Serial No. 713,308. In Great Britain March 7,

18 Claims.

This invention relates to the manufacture of cellulose from ligno-cellulosic materials, for example wood, straw and grass.

I have found that very satisfactory separation of the encrusting materials from the cellulose in ligno-cellulosic materials may be produced by treating or extracting them with organic solvents containing a carbonyl group and/or an ether group. I have further found that particularly satisfactory results may be obtained by employing two organic solvents of different polarities in admixture with each other, for example a mixture of a polar liquid and preferably a strongly polar liquid with a non-polar liquid, or a mixture of two polar liquids having different polarities, or in other words containing groups of different polarities.

As examples of organic solvents containing the carbonyl group may be mentioned methyl ethyl ketone and higher ketones, cyclic ketones such as cyclohexanone, methyl cyclohexanone or other ketonic substances, for example pyruvic acid and diacetone alcohol, aldehydes, especially aromatic aldehydes, lower fatty acids and particularly acetic acid and esters of organic carboxylic acids and especially of the lower fatty acids, for example methyl or ethyl formate or acetate. Amongst the acids available, formic acid is not so useful as acetic acid since under the temperature and pressure conditions which, as explained below, are preferred for effecting the extraction of the lignin and other encrusting substances, formic acid is liable to give rise to an undue amount of degradation of the cellulose. Among the solvents containing ether groups which may be used according to the present invention may be mentioned diethyl ether, ethyl propyl ether, di-iso propyl ether and cyclic ethers such as dioxane, methylene ethylene ether and ,homologues and derivatives of these cyclic ethers, for ex ample dimethyl dioxane. Substances which contain both carbonyl groups and especially ketonic groups and ether groups, for example tetrahydropyrone (1.4-oxanone) and its homologues and substitution products are also very useful. Particular attention is directed to the cyclic bodies containing carbonyl and/ or ether groups, for example the cyclohexanone and its homologues, 1.4-oxanone, dioxane and methylene ethylene ether mentioned above. The invention includes extracting theligno-cellulosic materials with any of the above solvents alone, but particularly valuable results are obtained by employing them in admixture with water.

As already indicated the invention further in- Y ether.

cludes extracting the ligno-cellulosic. materials with mixtures of organic liquids of different polarities. Thus, mixtures of alcohols, ketones, aldehydes, esters or acids may be employed'in admixture with non-polar organic solvents, for 5 example benzene, toluene, xylene or other hydrocarbons, carbon tetrachloride, hexa-chlorethane or similar non-polar chlorinated hydrocarbons. Again, mixtures of strongly polar liquids such as the alcohols, ketones, aldehydes, esters or acids 10 may be employed together with less strongly polar liquids such as the ethers, for example diethyl ether or di-iso propyl ether. Again, three or vmore organic liquids having different polarities may be employed, for instance mixtures of 5 methyl ethyl ketone or other 'ketones with ethers such as di-iso propyl ether and hydrocarbons or non-polar chlorinated hydrocarbons, or mixtures of ketones, for example methyl ethyl ketone, with cyclic ethers, for instance dioxane and hydro- 0 carbons or other non-polar solvents. Thus, I may employ a mixture of 90% ethyl alcohol and 10% benzene, a mixture of 40 to parts of dioxane with 60 to 40 parts of acetone, a mixture of 40 to methylene or ethylene chloride or 25 other polar chlorinated. hydrocarbons with 60 to 30% methyl, ethyl or isopropyl alcohol, or a mixture of 40 to 60 parts of acetone or alcohol with 60 to 40 parts of diethyl ether or diiso propyl able to have present at least one component which is soluble in water.

The ligno-cellulosic material is preferably subjected to the action of the solvents or solvent mixtures while in a finely divided form. For ex- '35.

ample wood may advantageously be employed in the form-of chips or even of a mechanical pulp. Preferably the treatment of the material is effected at a temperature considerably higher than atmospheric. Thus, for example, temperatures 40 between about 50 and 200 C., for instance between and or 0., may be employed; temperatures higher'or lower than these may, however, be employed if desired. Conveniently the process. may be'carried out under constant 45 volume conditions, for example in closed digesters or other vessels, so that the pressure au'tomat-- ically adjusts itself to the temperature employed.

It is desirable to ensure a thorough impregnation of the material by the solvent or'solven't mix- 50 ture. Thus, although the material may be simply agitated with the solvent or-solvent mixture under the conditions of temperatureand pressure described above, it is preferable to aid the impregnationz for example by first evacuating to any 55 Generally in such mixtures it is prefer- 30' 1931, such a process may be carried out by causing the sudden vaporization ,of a liquid within the material. Any other method of securing an efilcient contact between the material and the solvent or solvent mixture may be employed.

The treatment of the ligno-cellulosic material I with the solvent or solvent mixture may be effected in a single stage or two or multi-stage process and in a continuous or discontinuous manner. For example the extraction maybe per-' formed in digesters or vessels such as are commonly employed in pulping processes, for example in the sulphite process. In another method of carrying out the invention the material may be subjected to a continuous extraction with the solvent or solvent mixture; For example the material may be caused to travel through a reaction vessel .in a direction counter to that of a stream of solvent or solvent mixture.- In any case the so vent or solvent mixture may, after the treatment, be freed from lignin and other substances and returned to the process. For example the solvent or solvent mixture may be distilled 'ofl', leaving the lignin and other substances in the solid form. A

Other compounds capable of aiding the removal of lignin and othersubstances, for example by exercising a softening or slight destructive effect on the cellular structure of the materials, may

, also be present. Thus, for example, mineral acids or alkalies may be used in conjunction with the extractingliquor. Moreover, organic acids may be thus employed and may then act also as ex- I poses for which cellulose is used, for example for the manufacture of cellulose ethers, cellulose nitrate or cellulose xanthate, or for the manufacjected to treatment with lowerfatty acids if a lower fatty acid has not already been employed inthe extraction process. Again, a two-stage pretreatment may be applied such as that described in my U. S. Patent'No. 1,711,110 involving a preliminary treatment with hot dilute alkali or with cold strong alkali followed by a treatment with an organic acid and particularly a lower fatty acid. t Y

The following examples illustrate the inven- Example 1 Wood chips are mixed with s to 10 times their weight of a 50 to 60% aqueous solution of dioxane particularly if temperatures above C. or.

thereabouts are employed for the extraction step. Similarly, alkalies are liable to exert a degrading action upon the cellulose at high'temperatures, and it is preferable, in employing either.

mineral acids or alkalies to soften the materials,

to carry out the softening process as a pretreatment before the extracting step proper, and to .remove or substantially remove the acid or alkali used for the softening before carrying out the extraction step. Such removal may, for example, be efifected by washing with water or witha solvent, for example the solvent or'solvent mixture subsequently tobe ,used for the extraction. If desired the ligno-cellulosic material may be subjected to other treatments prior to extraction by the process of the present invention, for example to treatments to remove resins; Thus, a

simple extraction of the resins with benzene or benzene-alcohol mixtures may be applied. However, the resins are usually quite readily extracted in the process of the present invention, and such a procedure is generally unnecessary unless the lignin is required in a more or less purified form.

The cellulose produced by the process of the present invention may be employed, if, desired 7 after any th r treatment, for any of the PW" in an autoclave. are then heated to a; temperatureof 180 to 200 C. for-2 to 3 hours, after which the solvent may be withdrawn, preferably without reducing the pressure, and further solvent introduced. The extraction may thus be carried out in stages and. is generally complete after digestion with the solvent mixture for about 9 to 12 hours. In the second or later stages of the extraction the temperaturemay be increased somewhatgfor example to about 220 to 230 C. The cellulosic material remaining after the extraction may be washed, for example with water or with alcohol.

Example 2 Wood chips are sprayed with their own weight of a mixture of 30 parts of concentrated hydrochloric acid and 70 parts of glacial acetic acid and are allowed to remain at atmospheric temperature for 6 hours. After this period the cellulose washed thoroughly first with water and then with a mixture of di-iso propyl ether and'ethyl alcohol in equal parts by volume. The wood chips are then extracted as described in Example 1 with a mixture of equal parts by volume of iso propyl ether and ethyl alcohol.

Example 3 Wood chips are treated as described in Example 1 or 2 with the exception that the extractingliquid consists of a mixture of equal parts of methylene chloride and methyl alcohol and the temperature is maintained throughout the extraction at to C.

Y Example 4 Wood chips are treated as in Example 1 or 2 with the'exception that as extracting agent there,

The contents of the autoclave organic solvent containing an oxygen atom linked only to carbon, at a temperature above the normal boiling point of the organic solvent.

2. Process for the production of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction with a single organic solvent containing an oxygen atom linked only to carbon, at a temperature above the normal boiling point of the organic solvent.

3. Process for the production of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction with a single organic solvent containing a carbonyl group, at

a temperature above the normal boiling point of a 5. Process for the production of cellulose from.

lignocellulosic materials, which comprises subjecting the materials to extraction with an organic solvent containing an ester group, at a temperature above the normal boiling point of the organic solvent.

6. Process for the production of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction at an elevated temperature with a cyclic ether.

7. Process for the production of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction at an elevated temperature with dioxane.

8. Process according to claim 6, in which the organic solvent is employed in admixture with water.

9. Process for the production of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction with a cyclic ether, at a temperature above the normal boiling point of the cyclic ether.

10. Process for the production'of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction with a single organic solvent containing a keto group, at a temperature above the normal boiling point of the organic solvent.

11. Process for the production of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction with a single organic solvent containing an ester group, at a temperature above the normal boiling point of the organic solvent.

12. Process for the production of cellulose from lignocellulosic materials, which comprises subjecting the materials to extraction with a cyclic ether at a temperature above the normal boiling point of the solvent and under superatmospheric at a temperature above the normal boiling point of dioxane.

' 15. Process according to claim 2 in which the organic solvent is employed in association with water.

16. Process according to claim 4 in which the organic solvent is employed in association with water.

17. Process according to claim 5 in whichthe organic solvent is employed in association with water.

18. Process according to claim 9 in which the organic solvent is employed in association with water. 7

HENRY DREYF'US. 

